Answer: The answer is 105 ft. and 35 ft.
Step-by-step explanation: Given that Mauro has 140 ft. of rope, which he wants to cut into two pieces such that the length of the longer piece is 3 times the length of the shorter piece. We need to find the lengths of both the pieces.
Let 'x' and 'y' be the lengths of the longer piece and shorter piece respectively. Then, we will have the following system of equations.

Substituting the value of 'x' from the second equation in the first equation, we have

Thus, length of longer piece = 3 × 35 = 105 ft., and length of shorter piece = 35 ft.